Although it is widely accepted that chronic gingival inflammation resulting from plaque bacteria progresses to periodontitis with loss of alveolar bone and eventual loss of teeth, the factors that relate plaque-induced inflammation to destrution of adjacent bone are not well known. The objective of this proposal is to define the nature, origin, and actions of factors associated with dental plaque bacteria and/or chronic gingival inflammation which may affect resorption of alveolar bone. Approaches to this objective are: 1. A bone organ culture system will be used to detect and analyze bone-resorption stimulation by bacterial components and products, materials from cultured lymphocytes and other cells associated with the inflammatory response, and substances isolated from fresh or cultured gingiva. 2. Bones treated with active materials will be studied histologically to correlate morphologic changes with biochemical measurements of resorption. 3. Attempts will be made to purify and identify substances responsible for bone-resorption stimulation in active materials. 4. Current efforts to develop a suitable in vivo model system to test the significance of in vitro findings will be continued. These approaches are presently being used in studies of osteoclast activating factor, a bone resorbing factor from lymphocytes, and will continue to be a major part of this proposal.